Contact potential variable potential charger



Feb. 16, 1954 R. R. ANNIS ETAL 2,669,665

CONTACT POTENTIAL VARIABLE! POTENTIAL CHARGER Filed Aug. 21, 1952 IN V EN TORS FHCHARD R. ANNIS 'SIMON COHEN Y HOWARD HASELKORN Patented Feb. 16, 1954 CONTACT EPOTENTIAL POTENTIAL CHARGER Richard R. fiAmiis, Cdlb'rook, N. H., and Simon Cohen and Howard Haselkorn, Asbury Park, N. J.,assignors to the United States of America ES -represented by the Secretary of the Army Application August. 2\1,.1952,rSerial No. 305,-71-6 (Cl. 31"O--'6) (Granted under Title 35, II. :8. Code -i952),

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The inventiondescribed herein may manuf actured (and used by or :for the Government for governmental purposes, without the payment of any royalty thereon.

The present invention relates to an improved variable potential sourc'e a'nd more particularly to a device for charging instruments, such as quartz fiber dosimeters, of the electrostatic type.

Since most variable potential sources or devices for charging instruments of the electrostatic type utilize batteries, the reliability of the instruments depends upon the shelf life of the battery orbatteries utilized. Likewise the weight and size of the instruments is limited by the weight and size of the battery or batteries used.

An object of the present invention is to overcome the above and related disadvantages.

Another object is to provide a variable potential source having unlimited shelf life.

A further object is to provide a light weight, compact variable potential source.

A still further object is to provide a portable, compact, light weight, rugged device having an infinite shelf life for charging instruments such as quartz fiber dosimeters, of the electrostatic type.

These and other objects of the invention will become apparent from the description and claim that follow.

There is provided, in accordance with an embodiment of this invention, a variable potential source comprising a pair of opposed electrically conductive plates, each having a different work function. Terminal elements are connected to each plate, and a dielectric element is positioned between the plates. Means are operatively associated with the plates for simultaneously bringing them into contact with the dielectric element and for progressively increasing the spacing between the plates. The action is such that an initial contact potential is established between the plates and this initial potential is progressively increased in proportion to the spacing between the plates.

The invention will be more clearly understood by reference to the appended drawings wherein:

Figure 1 is a circuit diagram of a variable potential source in accordance with an embodiment of this invention, and

Figure 2 is a perspective view, in section, of a variable potential source in accordance with this invention utilizing an electrical circuit similar to that shown in Figure 1.

Similar parts are identified by like numerals throughout the drawings.

The variable potential source shown in Figures 1 and 2 includes two electrically conductive plates 2 and 4 of, for example, aluminum and copper, respectively, or any two other metals :having different work functions. A well 8, into which the instrument to be charged may be inserted, consisting of a central terminal T) connected by means of lead 9 to stationary plate 4, and a coaxial terminal '5' connected by means of lead 3 to movable plate '2 completes the basic circuit. Insula'ting :spacer I 8 positions terminal 5 within terminal 1.

.A'swit'ch 8 is provided in the lead 9 for opening and closing the circuit of Figure 1. Likewise, an electrometer I8 is provided in the circuit of Figure 1 'for measuring the output potential of the variable potential source.

In the variable potential source shown in Figure 2, plate 4 is fixed to plastic housing I while plate 2 is movable. The opposing surfaces of plates 2 and 4 are coated with dielectric coatings l0 and II, respectively. Coatings l0 and II may consist of a suitable dielectric material such as polytetrafluoroethylene, varnish, etc. The coatings l0 and II in addition to acting as a dielectric prevent oxidation of the plates 2 and 4 thereby increasing the efliciency of the device. A control knob 12 of insulating material is connected to threaded metallic bolt [5 which is secured to plate 2 by means of screw I3 for adjusting the spacing between the plates 2 and 4. Lead 3 is connected to metal block [4 which is electrically connected to movable plate 2 through bolt I5; and lead 9 is directly connected to stationary plate 4. A narrow raised lip is left uncovered along the periphery of both plates to allow the plates to be brought into electrical contact when they are moved together.

The well 6 illustrated in Figures 1 and 2 is particularly constructed for use in charging quartz fiber pencil type electroscopes, or dosimeters, of the type shown in Figure 9-4, page of Radiological Defense vol. 1, prepared by the Joint Crossroads Committee. Of course, other types of terminal arrangements may be utilized to suit the type of system to which energy (in the form of an electrical potential) is to be applied. If the instrument to be charged is of the self-reading type, no electrometer is required; however, when the instrument is of the non-self reading type the electrometer must be used to indicate the charge to which it has been subjected.

The initial voltage produced in the variable potential source of the present invention Vi is due to the contact potential that is developed between two metals each of which is characterized by a difierent work function. As the spacing D between the two plates 2 and 4 of the charger is varied the dielectric constant K of the device varies and so does the output voltage V0 between the plates 2 and 4. Since the output voltage V0 is directly proportional to the charge Q and inversely proportional to the capacitance C of where A equals the face area of plate 2 or plate 4. Thus, it may be seen that once the initial contact potential is established by causing the two plates to come into contact the output voltage V0 will vary directly with the spacing D, and inversely with the dielectric constant K. Dielectric constant K decreases as spacing D increases.

Further analysis of the system shows that the maximum output voltage V0 maxvaries with the initial contact voltage Vi, the initial capacitance C1 between the plates 2 and 4, and the capacitance C3 of the device being charged in accordance with the following formula:

Voltages of up to about 700 volts have been attained with the device of this invention. Most dosimeters of the quartz fiber type require about 140-200 volts for a complete charging.

As many apparently widely diiferent embodiments of the invention may be made without departing from the spirit and scope hereof, it is to '4 be understood that the invention is not limited to its specific embodiments except as defined in the appended claim.

What is claimed is:

A device for charging an electrometer comprising a pair of electrically conductive plates having different work functions, said plates being parallel to and facing one another, a layer of dielectric material coating the surfaces facing one another of said plates, said plates being provided with means for establishing a contact therebetween when moved together, means for moving said plates together to establish said contact whereby an initial contact potential is developed therebetween and for then moving said plates apart to increase the value of said potential, the last named means comprising a threaded shaft connected to one of said plates engaged with and movable with respect to a fixed member,

a terminal fitting into which said electrometer may be plugged connected to said plates, and a switch between said fitting and said plates for opening and closing the circuit therebetween.

RICHARD R. AN'NIS. SIMON COHEN. HOWARD HASELKORN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,577,446 Bosch Dec. 4, 1951 2,588,513 Giacoletto Mar. 11, 1952 OTHER REFEREN CES Electrical Charges by F. Sanford, 1919, Stanford University Press, pp. 89-94. 

